QAItemView: in MultiSelection, press deselects only if no drag can start

In MultiSelection mode, items are by default toggled on press, which
follows the example of standard Windows controls. However, when dragging
is enabled, then the press might be the beginning of a drag'n'drop
operation, and deselecting the item on press breaks the selection and user
experience.

Don't toggle the selection for presses on an already selected item that
might get dragged; instead, wait for the release event.

Extend the test case slightly to cover the special case. Dragging a
selection in a drag-enabled and MultiSelection item view wasn't possible
before either.

Fixes: QTBUG-59888
Change-Id: Ibd3e95a71ea63dd1e9bc3c8a723eafa9a1c21afa
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: David Skoland <david.skoland@qt.io>

1 files changed, 10 insertions, 3 deletions

diff --git a/src/widgets/itemviews/qabstractitemview.cpp b/src/widgets/itemviews/qabstractitemview.cpp
index f4f41e6f68..8a923e44a7 100644
--- a/src/widgets/itemviews/qabstractitemview.cpp
+++ b/src/widgets/itemviews/qabstractitemview.cpp
@@ -3981,16 +3981,23 @@ QItemSelectionModel::SelectionFlags QAbstractItemViewPrivate::multiSelectionComm
                 return QItemSelectionModel::Toggle|selectionBehaviorFlags();
             break;
         case QEvent::MouseButtonPress:
-            if (static_cast<const QMouseEvent*>(event)->button() == Qt::LeftButton)
-                return QItemSelectionModel::Toggle|selectionBehaviorFlags(); // toggle
+            if (static_cast<const QMouseEvent*>(event)->button() == Qt::LeftButton) {
+                // since the press might start a drag, deselect only on release
+                if (!pressedAlreadySelected || !dragEnabled || !isIndexDragEnabled(index))
+                    return QItemSelectionModel::Toggle|selectionBehaviorFlags(); // toggle
+            }
             break;
         case QEvent::MouseButtonRelease:
-            if (static_cast<const QMouseEvent*>(event)->button() == Qt::LeftButton)
+            if (static_cast<const QMouseEvent*>(event)->button() == Qt::LeftButton) {
+                if (pressedAlreadySelected && dragEnabled && isIndexDragEnabled(index) && index == pressedIndex)
+                    return QItemSelectionModel::Toggle|selectionBehaviorFlags();
                 return QItemSelectionModel::NoUpdate|selectionBehaviorFlags(); // finalize
+            }
             break;
         case QEvent::MouseMove:
             if (static_cast<const QMouseEvent*>(event)->buttons() & Qt::LeftButton)
                 return QItemSelectionModel::ToggleCurrent|selectionBehaviorFlags(); // toggle drag select
+            break;
         default:
             break;
         }